Wednesday, 2 June 2010

Being transparent (or nearly so) doesn’t mean animals have nothing to hide. On the contrary, their lack of pigmentation can help them elude predators who literally see right through them. Transparency also allows creatures to conserve precious resources, a benefit anyone can see.

Transparent Sea Cucumber

Slow moving, soft bodied bottom dwellers for the most part, Sea Cucumbers are an ancient lineage of sea creatures who have evolved a variety of ways to survive and thrive over hundreds of millions of years of evolution. For some Sea Cucumbers, being transparent allows them to fly under the radar, as it were, of predators in search of a quick & easy kill.

Lightly tinted in rosy pink, Enypniastes sea cucumbers live in the pitch-black ocean depths far below the 656-ft (200m) threshold where sunlight is unable to penetrate. The species was discovered in the northern Gulf of Mexico, 1.7 miles beneath the surface – before the current sub-sea oil spill occurred. Hope the li’l guy’s OK…

Transparent Butterfly

Butterflies of the species Greta Oto are commonly called clearwings or glasswings. It’s not that these butterflies have evolved transparent wings, more like they have dispensed with the growth of colored scales that normally cover the wings of butterflies and moths. Wash an average butterfly (well, imagine doing so) and you’ll end up with something that looks a lot like Greta Oto.

Glasswing butterflies are found from Mexico through Panama and have wingspans of 2.2 to 2.4 inches (5.6 to 6.1 cm) in width. It is thought that their mostly transparent wings make these butterflies less visible when in flight.

Transparent Goldfish

In late 2009, researchers at Mie University in Japan created a transparent goldfish by selectively breeding pale gold fish. The end result was a fish with translucent scales and skin through which many of the creature’s internal organs can be easily seen. “As this goldfish grows bigger, you can watch its whole life,” said Yutaka Tamaru, an associate professor at Mie University. That life could go on for some time as the non-gold goldfish are expected to live up to 20 years and grow to a length of 10 inches (25cm).

Though the general public will undoubtedly be clamoring for transparent goldfish to stock their home aquariums, the real reason the Mie University researchers created the transparent goldfish was to reduce, even negate, the need for dissections in school biology classrooms. This should make countless queasy students very, very happy – not to mention countless fish.

Transparent-Headed Barreleye Fish

The Pacific Barreleye (Macropinna microstoma) was first described in 1939 but specimens of this unusual deep sea fish suffered damage when raised to the surface through low-pressure shallow surface waters. In 2009, researchers at the Monterey Bay Aquarium Research Institute (MBARI) using remote-operated cameras were able to observe barreleyes in their element – 2,000 to 2,600 feet (600 to 800 meters) below sea level off the coast of central California. What they saw astonished them: the barreleye’s eyes rotate within a transparent, fluid-filled head shield.

Viewed head on, the barreleye’s face looks normal but what seem to be eyes are actually “nares” – the piscine equivalent of nostrils. The eyes are the vivid green structures located within the fish’s head, where they can be directed to look upwards while the fish remains horizontal.

Here is a video of the barreleye as first spied by MBARI’s seagoing ROV cameras:

Transparent Cave Crayfish

Caves are some of the darkest places on the planet – even sophisticated light-gathering instruments are unable to register a single photon in the deepest, darkest caves. Under these conditions, creatures including fish, spiders, insects and crayfish have evolved into “troglobites”: animals so precisely adapted to living in darkness that they cannot survive outside cave environments. Under such conditions, neither eyes nor pigmentation are necessary.

There are (at the latest count) 39 species of cave crayfish species in North America, some restricted to the isolated caves in which they evolved. Cave crayfish range from whitish albinos to nearly translucent in appearance. If their chitinous exoskeletons were as thin as skin they would certainly be considered to be transparent.

Transparent Squid

Squid of the family Cranchiidae number around 60 species and are commonly known as Glass Squids. Indeed, these robustly built but delicate looking cephalopods outwardly resemble hand blown glass bottles with the only pigmented part being the cigar-shaped liver. Glass squids come in a wide range of shapes and sizes, and include the Colossal Squid that can grow up to 9.8 feet (3m) long – not including the arms.

Glass squid are near-invisible for the most part, but sometimes they want to be seen… at mating time, for instance. That’s when heretofore hidden chromophores blaze into action, bathing the squid in undulating waves of eerie bioluminescent light.

Transparent Jellyfish

Jellyfish can be found in all of the world’s oceans and, if the predictions of some scientists can be believed, are increasing in number as the oceans warm up. Jellyfish are often transparent to some degree, often appearing as thin films that serenely undulate amongst schools of fish who don’t see them… until it’s too late.

Like glass squids and other deep sea marine animals, certain species of transparent jellyfish use bioluminescence to attract prey close enough for the jellyfish’s tentacles to shock them into submission. The Comb Jelly above displays pretty rainbow colors – fatal attraction indeed!

Transparent Flounder

Many marine creatures employ transparent body tissues in their larval stages in order to help secrete themselves from bigger predators, and fish are no exception. The young flounder above enhances its translucence by virtue of having a flat, thin body plan.

Flat, tasty and transparent is no way to go through life, so as a young flounder grows it will turn to another way of disguising itself – camouflage. As for its pancake shape, it continues to provide an advantage by helping the flounder keep a low profile on flat, sandy seafloors (and, presumably, the floors of certain frat houses).

Transparent Salp

Once dismissed as being a rather unsophisticated, primitive form of sea life, salps are now credited with being one of the most efficient carbon sequestering organisms on the planet. Scientists estimate as much as 1/3 of all human-created CO2 is being processed by salps, who constantly eat phytoplankton and expel compact fecal pellets rich in carbon that rapidly sink to the ocean floor.

Salps are almost completely transparent, with only their constantly full stomachs breaking the pattern. Salps are normally solitary creatures but have been known to link together in elaborate chains as shown above.

Transparent Frog

In late 2007, a research team from the Institute for Amphibian Biology at Hiroshima University in Japan announced it had successfully created transparent frogs. According to Professor Masayuki Sumida of the IAB, “Transparent frogs will prove useful as laboratory animals because they make it easier and cheaper to observe the development and progress of cancer, the growth and aging of internal organs, and the effects of chemicals on organs.” All this without causing the frogs to, er, croak.

Umm, not so fast, prof… have you seen the “glass frog” (above), native to the Venezuelan rainforest? Like the transparent frogs selectively bred in the lab from generations of pale-skinned Japanese Brown Frogs, the Glass Frog’s internal organs and eggs can be seen without too much trouble. Word to Professor Sumida: take the grant money and run!

As we have seen, the vast majority of transparent creatures live in the sea – see-through butterflies, crayfish and frogs are much less common and the latter do not occur naturally. Will scientists pursue the lines of experimentation that brought about transparent goldfish and frogs to their logical conclusion? Time will tell… and some day we may end up questioning the old maxim, “beauty is only skin deep”.